Aljazeera's correspondent reported the six were killed in the bombing on Monday in the Balad Ruz area of Baquba.
Qaisar Hamid, a hospital official in the area, said 18 people were injured in the attack, including the deputy governor of Diyala province, Aqil Hamid al-Adili, whose wounds were described as light.
The hospital said it had received two of the dead.
Police Brigadier Daud Mahmud said the attack was made with a booby-trapped car, adding that police were busy moving casualties to the hospital.
US occupation military spokesman Major Neal O'Brien said the blast occurred at about 7.30am (0330 GMT).
Diyala's deputy governor
narrowly escaped death
Occupation troops moved to the scene of the attack to support Iraqi police in conducting an assessment and to assist in evacuating casualties, he said.
Iraqi fighters in Baquba have killed scores of police and local officials appointed by the US occupation force since the fall of Saddam Hussein last year.
A massive car bomb at the end of June in front of a police station in the centre of the city killed 70 Iraqis, mostly those who had lined up to join the police.
Meanwhile a US marine was killed in action in western Iraq, the occupation military said on Monday.
A statement said the marine was killed on Sunday in al-Anbar province, which includes the towns of Falluja and Ramadi.